The extracts can be dried in a spray drier, freeze drier or a drum drier.
a. Spray drying. Spray drying requires that the concentrated coffee solutions extracted are ‘atomized’ to form droplets (10-200 micrometers in diameter) and then sprayed into a current of heated air (150-300ºC) in a large drying chamber, this is usually a concurrent air flow.
Complete and uniform atomization is required. For coffee drying, a centrifugal atomiser is usually used. The liquid is fed to the middle of a rotating bowl (peripheral velocity of
90-200m/s). This produces droplets with diameters of 50-60 micrometers in a uniform spray.
The droplets are dried very rapidly (1-10 seconds) due to the very large surface areas. The dry powder is removed from the base by a screw conveyor or a pneumatic system.
b. Freeze drying. Freeze drying takes place by sublimation (ie a solid material transforming directly to vapour without passing through a liquid stage). The coffee solution is slowly frozen in conventional freezing equipment. The frozen material is put under reduced pressure and heated. As long as the pressure in the freeze drier is below the vapour pressure at the surface of the material, it will sublime directly to vapour without melting. The vapour needs to be removed by a vacuum pump and is condensed on refrigeration coils. The final drying stage involves evaporative drying (desorption). This is achieved by raising the temperature to near ambient whilst retaining the low pressure.
Coffee needs to be frozen as a foam (by gas inclusion) to prevent formation of a glassy vitreous frozen material.
c. Drum drying. This is rare nowadays. It involves the extracts being dried by direct contact on a heated cylindrical surface.
Packaging and Storage
- Materials. Packaging of coffee (especially if it is ground) requires polypropylene. Polythene cannot be used as the flavor components diffuse through it. The use of laminates is popular but more expensive. Glass is also a suitable container.
- Simple sealing. Polypropylene bags can be sealed using simple hand-operated electric sealing machines.
- Storage. The optimal conditions for storage are low temperature, low humidity and pest-free in a shaded area. To prevent pests entering the store, the roof should be completely sealed. Mosquito netting should be placed over the windows, and the doors should be close-fitting.
- Coffee pulp. If not treated, this will give rise to unpleasant odours and attract flies and insects. It can be converted into animal feed, soil conditioner, or used for caffeine extraction and biogas production.
- Waste water. Care needs to be taken to prevent water from the processing, polluting local rivers or lakes.
Conlins Coffee Company
2753 Park Avenue, Pasay City
Metro Manila, Philippines 1300
Phone: (63 2) 551-3216, (632) 8312729
Fax: (63 2) 834-1605
Cellphone: (63 916) 5294052
Service: (63 917) 8315155 Service and Support
Sales: (63 917) 8315144
Cape Australia: Coffee-Processing Machinery
179 Broken Head Road
Newrybar, NSW, Australia 2479
Tel: +61 2 6687- 1004, Fax: +61 2 6687-1335
Email: [email protected]
John Gordon Co Engineers Limited
Hillcrest House, 4 Market Hill
Maldon, Essex, CM9 4PZ, United Kingdom
Tel: +44 (0) 1621 858944
Fax: +44 (0) 1621 857733
E-mail: [email protected]
Autopack Machines Pvt Ltd
101-C, Poonam Chambers, Dr. Annie
Besant Road, Worli, Bombay – 400 018. India
Tel: +91-22-24964926 / 24910593
Fax: +91-22-24924806 / 24974800 / 24934406
Email: [email protected], [email protected]
source: www.practicalaction.org, photo from freedigitalphotos.net